Caption: Cell structure. Light micrograph of cultured endothelial cells. Fluorescent dyes have been used to show the cell structure. Nuclei (round) contain the cells' genetic information, DNA (deoxyribonucleic acid) packaged in chromosomes. Actin filaments (orange) are part of the cell cytoskeleton, which is responsible for intracellular transport, structure and motility of the cell, as well as segregating the chromosomes during nuclear division. Actin is the most abundant cellular protein. Endothelial cells are flat and line all the body's blood vessels.